The most fuel-efficient Lexus IS 250 is the 2013 Lexus IS 250 Base which gets 21 MPG City and 30 MPG Highway.
It is important to remember factors such as driving style, weather conditions, and the use of features such as Eco mode can impact fuel efficiency. Fuel economy figures are based on EPA estimates for when vehicle sold as new. Fuel economy may vary for reasons like driving conditions and vehicle history. Unless specified, figures are for vehicles equipped with an automatic transmission. See fueleconomy.gov.